Single-atom catalysts (SACs) based on earth-abundant metals are crucial for energy-related applications due to their cost-effectiveness and sustainability. This review discusses the application of SACs in electrochemical energy storage and electrocatalytic conversion of chemicals to fuels or high-energy products. The oxygen reduction reaction (ORR) is particularly important in fuel cells and metal-air batteries. Transition metal SACs are analyzed for two- and four-electron reaction pathways, with a focus on electrochemical water splitting for green hydrogen and ammonia production via nitrogen reduction. The review covers various energy storage systems, including lithium-based batteries, metal-air batteries, and metal-sulfur batteries, highlighting the role of SACs in enhancing performance and efficiency. SACs in supercapacitors are also discussed, emphasizing their ability to improve redox kinetics and interaction with reactants. The review highlights the potential of SACs in reducing energy barriers and improving reaction efficiency. SACs are particularly effective in lithium-ion and lithium-metal batteries, where they enhance electrochemical performance, reduce dendrite formation, and improve cycle stability. In metal-air batteries, SACs are crucial for improving ORR and OER performance, with examples like Fe-N-C and Co-N-C SACs showing significant improvements over traditional catalysts. The review also discusses the challenges in scaling up SAC synthesis and the importance of developing sustainable and recyclable catalysts. Overall, SACs offer a promising solution for sustainable energy storage and conversion, with potential applications in electric vehicles, grid storage, and renewable energy systems.Single-atom catalysts (SACs) based on earth-abundant metals are crucial for energy-related applications due to their cost-effectiveness and sustainability. This review discusses the application of SACs in electrochemical energy storage and electrocatalytic conversion of chemicals to fuels or high-energy products. The oxygen reduction reaction (ORR) is particularly important in fuel cells and metal-air batteries. Transition metal SACs are analyzed for two- and four-electron reaction pathways, with a focus on electrochemical water splitting for green hydrogen and ammonia production via nitrogen reduction. The review covers various energy storage systems, including lithium-based batteries, metal-air batteries, and metal-sulfur batteries, highlighting the role of SACs in enhancing performance and efficiency. SACs in supercapacitors are also discussed, emphasizing their ability to improve redox kinetics and interaction with reactants. The review highlights the potential of SACs in reducing energy barriers and improving reaction efficiency. SACs are particularly effective in lithium-ion and lithium-metal batteries, where they enhance electrochemical performance, reduce dendrite formation, and improve cycle stability. In metal-air batteries, SACs are crucial for improving ORR and OER performance, with examples like Fe-N-C and Co-N-C SACs showing significant improvements over traditional catalysts. The review also discusses the challenges in scaling up SAC synthesis and the importance of developing sustainable and recyclable catalysts. Overall, SACs offer a promising solution for sustainable energy storage and conversion, with potential applications in electric vehicles, grid storage, and renewable energy systems.